Tunnel and Underground SpaceISSN:1225-1275(Print) 2287-1748(Online)한국암반공학회

In-situ stress evaluation of deep rock masses is a critical factor for the stability and constructability of high-level radioactive waste disposal facilities. In this study, in-situ stress in deep rock masses was evaluated through Cavity Contraction Creep (CCC) tests using a High-Pressure Dilatometer (HPD). The in-situ stress evaluation was conducted in a borehole at 757.3 m depth in the Wonju, using a 73 mm High-Pressure Dilatometer manufactured by Cambridge Insitu. Tests were performed at five locations up to 450 m depth. The CCC test is a method for determining in-situ stress by measuring pressure and displacement at the cavity wall and analyzing creep movement and creep rate. This method has the advantage of simultaneously evaluating in-situ stress while measuring the deformation modulus of rock masses. Test results showed maximum horizontal stress of 3.29 MPa and minimum horizontal stress of 2.06 MPa at 101.5 m depth, and maximum horizontal stress of 12.63 MPa and minimum horizontal stress of 8.83 MPa at 449 m depth, confirming the trend of increasing stress with depth. When compared with hydraulic fracturing test results conducted in the same area, the CCC tests yielded relatively lower horizontal stress values, which was attributed to the characteristic of CCC tests that do not induce rock failure. Although CCC tests have limitations such as subjectivity in creep analysis and the importance of equipment calibration, they can be utilized as a useful alternative method for determining the range of in-situ stress in deep rock masses in conjunction with conventional hydraulic fracturing methods.